One of the most valuable characteristics of polyolefins as a class of materials is versatility. They can be tailored to many fabrication methods to provide products such as fibers, films, molding resins, etc. which have excellent physical and chemical properties for a particular application. A large number of additives are used in polymer technology to improve, strengthen or otherwise alter the polymer, such that additives used in preparing a polymer are often a critical factor in commercial success of the final product.
Many specially tailored polymers employ free radical generators such as organic peroxides as an additive, for example to lightly crosslink polyethylene, or to visbreak polypropylene, predetermined amounts of organic peroxides are added to the polymer. As used herein, the term "visbreak" is taken to serve as evidence for chain scission of the polymer. Additional chemical additives such as antioxidants, antistats, flame retardants, light stabilizers, etc. are also employed is these polymers to prevent oxidation, discoloration, static charge, or thermal degradation during subsequent melting processes which the polymer must undergo. For example, it is well known that polyethylene melt flow reduction, which can be achieved by addition of organic peroxides, is effective for improving bubble strength for blown film applications. Likewise, it is known that polypropylene visbreaking, which also can be achieved by addition of organic peroxides, is effective for obtaining narrower molecular weight distribution and enhanced flow characteristics. Use of organic peroxide additives in combination with certain other additives such as antioxidants, and light stabilizer additives, however, has resulted in undesirable color and odor in the polymers containing the multiple additives.
Accordingly, it is an object of this invention to eliminate the above mentioned color and odor problems associated with polymers containing multiple additives.
It is a more specific object of this invention to provide a process for producing olefin polymers having desirable physical properties without impairing color or odor characteristics of the polymer.
It is another object of this invention to provide a continuous or batch process which will reduce the quantity of free radical generator required to modify a polymer to a desired viscosity.
It is another object of this invention to provide a polymer admixture process which is safe, simple, effective and economical.
A further object of this invention is to provide polymers which have improved processability.